St Catherine's Castle (Cornish: Kastel S. Kattrin) is a Henrician castle in Cornwall, built by Thomas Treffry between approximately 1538 and 1540, in response to fears of an invasion of England by France and the Holy Roman Empire. The D-shaped, stone fortification, equipped with five gun-ports for cannon, overlooked the mouth of the River Fowey in Cornwall. It was protected by a curtain wall and the surrounding cliffs. The castle remained in use for many years until it was closed at the end of the Napoleonic Wars in 1815. Brought back into service in 1855 during the Crimean War, it was fitted with two new artillery positions, but it soon became obsolete and was abandoned. During the Second World War the castle was refortified and used to house a battery of naval guns, protecting the coast